This invention relates to a method of offset printing on a polypropylene resin case for a video tape cassette.
Polypropylene resin sheets are being used in great quantities for paper holders, cases for video tape cassettes, and various other articles. Particularly in recent years, the use of this sheet material for cases of video tape cassettes has been increasing rapidly. Printing must be carried out on cases of video tape cassettes, but printing on the surface of polypropylene resin is extremely difficult. In the present state of the art, printing on surfaces of polypropylene resin is limited to silk screen printing with the use of epoxy resin ink.
Unfortunately, silk screen printing is accompanied by a number of problems such as low productivity, high cost, low printing accuracy, limited patterns, and the necessity of repeating printing for every color in the case of multicolor printing since only single-color printing can be carried out by this printing technique.
Accordingly, if an effective method of printing on polypropylene resin surfaces by a generally known offset printing technique could be devised and developed, the above enumerated problems would be solved, and the method would be advantageous in numerous aspects.